The present invention relates to a belt retractor for vehicle safety belts, comprising a belt pretensioner acting on the belt drum and having a linear drive, and a transmission means for converting the linear movement of the linear drive into a rotary movement.
Such a belt retractor is integrated with the belt pretensioner as a single assembly. In U.S. Pat. No. 4,423,846 a number of designs of such an assembly are described. On tripping the belt pretensioner the movement of the piston of the pyrotechnical linear piston and cylinder drive unit is transmitted via a cable to a pulley whose periphery is engaged by the cable. This pulley is then caused to rotate by the tension exerted by the cable and at the start of such rotation it is drivingly coupled with the belt drum. The cable and the pulley constitute a transmission means for converting the stroke of the piston into rotation of the belt drum. Owing to the rotation of the belt drum there is a tightening of the belt webbing. The angle of rotation necessary for a sufficient tightening of the belt requires a relatively large stroke of the piston. The cylinder of the piston and cylinder unit has to be made with a corresponding length so that the assembly consisting of the belt retractor and the belt pretensioner needs a correspondingly large amount of space in the vehicle.
A primary object of the present invention is to improve a belt retractor of the type referred to above so that a short working stroke of the linear drive is sufficient to achieve the desired pretensioning of the webbing, thus permitting a more compact design of the retractor/pretensioner unit.